Keyboard shortcut for inserting Unicode or UTF8

What keyboard shortcut should I use in order to insert a special character by typing its Unicode or UTF8?

Most people would use the Character Palette (Edit > Special Characters), but if you want to use the number, you go to system prefs/international/input menu and check the box for Unicode Hex Input, plus the box for "show input menu in Finder." The you select Unicode Hex Input in the "flag" menu at the top right of the Finder, hold down the Option/alt key, and type the Unicode hex code for your character.

If you tell us what character exactly you need, we may be able to tell you other ways to input it from one of the other keyboard layouts.